1. Field of the Invention
The present invention generally relates to toners used for document imaging and methods for making the toners. More particularly, the invention relates to an ultraviolet security toner that can be used in printers designed to use chemically prepared toner and that fluoresces when subjected to ultraviolet or near ultraviolet light.
2. Description of Related Art
Toner-based document imaging, such as electrophotographic, iongraphic, magnetographic, and similar imaging techniques, generally involves forming an electrostatic or magnetic image on a charged or magnetized photoconductive plate or drum, brushing the plate or drum with charged or magnetized toner, transferring the image onto a substrate such as paper, polyester film, or the like, and fusing the toner onto the substrate using heat, pressure, and/or a solvent. Using this technique, relatively inexpensive images can be formed relatively easily and quickly on a surface of the substrate.
Recently, toners have been developed for use in document security, such as ultraviolet security toners. Images formed by an ultraviolet toner may appear colorless when viewed under normal lighting but will fluoresce when subjected to an ultraviolet light. The ultraviolet images can provide document security in a variety of ways. As an example, a company may print checks including the payment amount using both traditional toner (such as black toner) and ultraviolet security toner. Upon receipt, a bank teller may view the check under an ultraviolet light in order to compare the printed payment amount in traditional toner to the printed payment amount in ultraviolet security toner. If the printed values differ, the teller will know that the check has been altered and should not be accepted.
Toners, including ultraviolet toners, may be formed conventionally or chemically. Conventional toners are typically manufactured using size reduction methods in which materials are melt mixed and systematically reduced in size to form the toner. As shown in FIG. 1, an X times magnified image of a conventional toner 100 formed by size reduction, particles 102 having uneven sides and edges that define craters.
Recently, companies have been developing chemically prepared toner (CPT) as an alternative to preparing toners for size reduction. CPT toners are manufactured using synthesis techniques in which the toner particles are developed and grown into the desired particle size and shape. As shown in FIG. 2, an X times magnified image of a CPT toner 200, particles 202 of the CPT toner 200 are generally spherical in shape.
With reference to FIGS. 1 and 2, the uneven edges and sides of the particles 102 of the conventional toner 100 cause reduced flowability, as compared to the spherical particles 202 of the CPT toner 200. The charge distribution of the CPT toner 200 is typically more uniform than the charge distribution of the conventional toner 100 as a result. Printers are typically designed to use only either conventional toners or CPT toners. The two are not compatible due at least in part to the difference in flow characteristics and charge distribution. The improved flow and charge distribution of a CPT toner allows the CPT toner to be used in printers used for printing higher quality images.
The process of conventional toner manufacturing is well documented and has been used in the art for decades. Equipment used to manufacture conventional toner is readily available and has a much lower initial cost than equipment for manufacturing CPT toner. Both types of toners provide advantages: conventional toner provides the advantage of being relatively inexpensive while CPT toner provides the advantage of producing a higher print quality.
For the foregoing reasons, improved conventional ultraviolet toners that are relatively inexpensive to make and provide improved print quality are needed.